Low yellow index polymer compositions, polymerizable compositions and lenses using said compositions

ABSTRACT

The present invention relates to new polymer compositions for use in the manufacture of opthalmic lenses which result from the copolymerization of a component (A) comprising at least 50% by weight of a monomer or mixture having formula ##STR1## wherein R 1  and R 2  are selected from H and C 1  -C 6  alkyl radical, 
     X is --O--, --S--, --SO 2 , --CO--, --CH 2  --, --CH═CH--, or C(CH 3 ) 2 , 
     m and n are integers and m+n ranging from 0 to 10 and 0,5 to 15% by weight of a component (B) comprising a monomer having an ethylenic unsaturation which does not contribute to an aromatic system and having a free hydroxy group in position α of the unsaturation, as well as to their use in opthalmology and to apparatus using these lenses, such as eyepieces and film/video camera optics.

This application is a continuation-in-part of U.S. application Ser. No. 08/172,127, filed Dec. 21, 1993, now U.S. Pat. No. 5,442,022. This application claims priority based upon French application No. 92 15533, filed Dec. 22, 1992.

The present invention relates to new polymer compositions for use in the manufacture of opthalmic lenses, to their use in opthalmology and to apparatus using these lenses, such as eyepieces and film/video camera optics.

Opthalmic plastics obtained from acrylic bisphenol A derivatives are in general too yellow for use.

The use of additives which reduce yellowness is well known, but usually at the cost of the degree of polymerisation and thermomechanical properties.

Opthalmic lenses may be produced in their final shape by casting polymerisable compositions between two moulds having the required surface geometries, then polymerising. A lens is then obtained with its two surfaces in their final state.

In order to reduce the need for large stocks of opthalmic lenses, semi-finished lenses are often made which have one moulded side only in its final geometry, the second side being finished when required.

Finishing the second side raises the temperature of the semi-finished lens and it is therefore vital that the polymer constituting the lens is sufficiently rigid and non-deformable at the temperature attained. The polymer must therefore have good thermomechanical properties.

The applicant has discovered that it is possible to produce polymers for the manufacture of opthalmic lenses in accordance with the invention which have good thermomechanical properties and a low yellow index making them particularly suitable for use in the manufacture of opthalmic lenses from a copolymerisable composition comprising at least one monomer having formula ##STR2## and a monomer derived from ally alcohol. This composition constitutes an object of the invention.

Monomers having formula I are known and some of their derivatives have already been recommended for use in opthalmology (GB-A-1 514 810, FR-A-2 431 511). In the latter document, monomers having formula I are used with monomers which are copolymerisable by a radical mechanism, wherein the homopolymer has an index greater than or equal to 1.55 to produce high index lenses.

Polymers produced from a monomer having formula I and the copolymers described in FR-A-2 431 511 are, however, too yellow to be usable in opthalmology without modification.

The invention consists in polymers constituted by units derived from monomers having formula I and allyl alcohol derivatives.

The invention further consists in polymerisable compositions comprising monomers having formula I and allyl alcohol derivatives.

The invention further consists in opthalmic lenses produced from these polymers, their use in opthalmology and apparatus containing these optics.

Further objects of the invention will become apparent from the following description and examples.

A polymer composition in accordance with the invention is characterised in that it is obtained by polymerisation of a polymerisable composition comprising:

(A) a component A comprising:

at least 50% and preferably 70 to 100% by weight of a monomer or mixture having formula I ##STR3## wherein R₁ and R₂ independently of each other may represent hydrogen or a low C₁ -C₆ alkyl radical, X represents ##STR4## m and n are integers and the sum m+n being between 0 and 10, inclusive of 0 and 10 and

0 to 50% by weight of one or more mono- or polyfunctional vinyl, acrylic or methacrylic comonomers (II);

(B) a component B in a proportion of 0.5 to 15%, preferably 1 to 5% by weight with respect to the weight of monomers (I) and (II) of a monomer (III) comprising an ethylenic insaturation which does not contribute to an aromatic system and containing in position α of this unsaturation, a carbon atom carrying a free hydroxy group and preferably linked to at least one hydrogen atom.

The ethylenic unsaturated monomers (III) used according to the invention are preferentially selected from the monomers having formula (IV). ##STR5## wherein R₃ and R₄ represent hydrogen or one of the groups R₃ and R₄ represent hydrogen while the other forms with group R₇ a C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups or one or more C₂ -C₄ alkylene groups; or one of groups R₃ and R₄ may represent hydrogen while the other represents an aliphatic C₁ -C₆ alkyl group, a cyclic C₄ -C₁₆ hydrocarbon group or an aromatic C₆ -C₁₆ hydrocarbon group;

R₅, R₆ and R₇, independently of each other, represent hydrogen or a C₁ -C₆ alkyl group which may be substituted by one or more OH groups, and wherein the chain may be interrupted by one or more other, ester or ketone groups; an aromatic C₆ -C₁₆ hydrocarbon group or a cyclic C₄ -C₁₆ hydrocarbon group;

R₇ may form with one of the groups R₃ or R₄ and C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups or one or more C₂ -C₄ alkylene groups;

R₅ and R₆ may form a C₅ -C₁₀ ring which may be substituted by one or more C₁ -C₄ alkyl groups or C₂ -C₄ alkylene groups;

two or more of the carbon atoms of the C₅ -C₁₀ ring formed with R₃ or R₄ and R₇ or with R₅ and R₆, may be bonded by a hydrocarbon bridge.

In accordance with the invention, the C₁ -C₆ alkyl group preferably represents a methyl or ethyl group.

Particularly preferred monomers having formula I are those wherein R₁ denotes CH₃ and R₂ denotes hydrogen and X represents ##STR6## and m+n is a whole number between 2 and 7, inclusive of 2 and 7. Particularly preferred monomers having formula III are those wherein R₃ and R₄ represent hydrogen, R₅ represents methyl, R₆ represents hydrogen or methyl and R₇ represents hydrogen, methyl, ethyl or CH₂ OH.

Preferred polymers are those wherein the monomer having formula I is 2,2-bis (4-methacroyloxydiethoxyphenyl)propane.

Monomers having the formula II may be aromatic of non-aromatic.

The following monofunctional aromatic compounds may be cited: phenyl(meth)acrylate, benzyl(meth)acrylate, phenoxyethyl(meth)acrylate, styrene.

The following non-aromatic compounds are preferred: an monofunctional alkyl(meth)acrylate such as methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate or isobutyl(meth)acrylate or difunctional derivatives such as butanedioldi(meth)acrylate, or tri-functional derivatives such as trimethylolpropane tri(meth)acrylate.

Particularly preferred monomers having formula IV are allyl alcohol, methallyl alcohol, crotyl alcohol, 2-cyclohexene 1-ol, trans 2-hexene 1-ol, cis 2-butene 1,4-diol, 3-methyl 2-butene 1-ol, trans 2-methyl 3-phenyl 2-propane 1-ol, 3-butene 2-ol, carveol, myrtenol, verbenol and trans-cinnamyl alcohol.

Polymerisation is effected in a known manner using an initial mixture containing the various monomers of the polymerisable composition, the polymerisation reaction being catalysable using catalysts such as benzoyl peroxide, cyclohexyl peroxydicarbonate, diisopropyl peroxydicarbonate or 2,2'-azo-bis isobutyronitrile. The catalysts are used in quantities sufficient in proportions of between 0.001 and 1% by weight with respect to the total weight of the polymerisable composition.

Opthalmic lenses are prepared by introducing the desired composition containing the various monomers described above into an apparatus constituted by a glass two-part mould and initiating a thermal polymerisation cycle of 10 to 20 hours duration at about 45° C. to 90° C., preferably about 50° to 85° C. It is also possible to polymerise photochemically or by induction heating using electromagnetic radiation, such as microwaves (2 450 MHz or 915 MHz) or high-frequency radiation (3.56 MHz; 27.12 MHz or 40.68 MHz).

Polymerisation by induction heating is normally completed in a period of less than one hour.

The polymer lens thus produced is then annealed for a period and at a temperature sufficient to eliminate residual stresses in the lens. The temperature is generally between 100° and 120° C. and annealing is carried out for about 1 to 5 hours.

It is also possible to effect polymerisation using moulds with one surface conforming to the final lens geometry and a second surface which does not conform to the final lens surface geometry but produces a second lens surface which can be finished when required.

The invention also consists in a polymerisable composition as defined above when used in the preparation of polymer compositions.

The polymers thus obtained, particularly following moulding, may be used to produce opthalmic components such as opthalmic lenses, spectacle or eyepiece lenses, and the optics of various devices including cameras, film/video cameras and microscopes, for example.

The yellow index is determined spectroscopically and visually. A standardised method is used to determine the yellow index by the spectroscopic method (ASTM D-1925-63). The yellow index is defined as follows: ##EQU1## where X, Y, Z are trichromatic coordinates of the sample measured using a UV-visible spectrophotometer scanning the spectrum from 380 to 780 nanometers, Yi is determined after annealing.

The visual method uses four standard glass samples containing increasing quantities of yellow dye to establish a range of yellows. Samples are classified according to their respective levels of yellow.

The degree of polymerisation is determined by measurement of the near infrared peak for the methacrylic group double bond by observing the area of the 6160 cm⁻¹ peak which corresponds to the first harmonic of the terminal methylene group CH bond vibration. The degree of polymerisation is given by: ##EQU2##

Thermomechanical properties are determined using a three point bending TMA apparatus. Lens rigidity is characterised by the high temperature moduli in the rubber-like region.

The following examples illustrate but do not limit the scope of the invention.

In each case an initial mixture was prepared by homogenisation for one hour of specific amounts of tetraethoxy bis-phenol A dimethacrylate sold by AKZO under the trade name Diacryl 121 and, if required, methacrylic monomers (ethyl methacrylate, butanediol dimethacrylate). Cyclohexyl peroxydicarbonate was used as catalyst in a proportion of 0.5% with respect to the total formulation.

Allyl alcohol derivatives having formula IV were introduced in the proportions indicated below just before casting into an apparatus constituted by two two-part glass moulds and an EVA gasket. The assembly then underwent an 18 hour thermal cycle starting from a temperature of 48° C. and arriving at 85° C. after 16 hours.

The polymerised articles thus produced were annealed for three hours at 110° C. before measurement of their properties.

The final articles have a thickness of 2 mm.

EXAMPLE 1

A mixture as described above was prepared by homogenising tetraethoxy bis-phenol A dimethacrylate sold by AKZO under the trade name Diacryl 121 and ethyl methacrylate in proportions of 92 parts Diacryl 121 to 8 parts ethyl methacrylate with stirring. This mixture was catalysed with 0.5% by weight of cyclohexyl peroxydicarbonate (CHPC). A composition having the following formula IV was then introduced into the resulting composition: ##STR7## wherein R₃, R₄, R₅ and R₆ have the meanings shown in the table below.

                                      TABLE I                                      __________________________________________________________________________     Additives  R.sub.3                                                                          R.sub.4                                                                          R.sub.5                                                                           R.sub.6                                                                           R.sub.7                                                                             mass %                                                                              Yi visual                                                                             E (MPa)                                  __________________________________________________________________________     ref                       0    2.95                                                                              3   47                                       allyl alcohol                                                                             H H H  H  H    2    1.62                                                                              2   58                                       methallyl alcohol                                                                         H H Me H  H    0.99 1.47                                                                              2   67                                       crotyl alcohol                                                                            H H H  H  Me   1.08 1.64                                                                              2   57                                       trans 2-hexene 1-ol                                                                       H H H  H  Et   2    1.81                                                                              2   60                                       cis 2-butene 1,4-diol                                                                     H H H  H  CH2OH                                                                               2    1.53                                                                              2                                            3-methyl 2-butene 1-ol                                                                    H H H  Me Me   0.98 1.36                                                                              2                                            cyclo 2-hexene 1-ol                                                                       H C H  H  C    2.06 1.64                                                                              2   59                                       __________________________________________________________________________

C represents a cycle

"Yi" is the yellow index, "visual" is the visually determined index; B represents the modulus of elasticity in the rubber-like region (150° C.).

In each case, a considerable reduction in the yellow index and improvement in mechanical properties were observed.

EXAMPLE 2

The polymerisable composition of example 1 was used with the same catalyst in the proportions indicated in example 1. The following results were obtained:

                  TABLE II                                                         ______________________________________                                                                          E      E                                      additive      %      Yi     p    (100° C.)                                                                      (150° C.)                       ______________________________________                                         allyl alcohol 0      2.95   93   57     47                                     allyl alcohol 0.55   2.16   93                                                 allyl alcohol 1.01   1.95   94                                                 allyl alcohol 1.51   1.89   97                                                 allyl alcohol 2      1.54   95          58                                     allyl alcohol 2.45   1.48                                                      allyl alcohol 3      1.48                                                      2-methyl 2-propene 1-ol                                                                      0.98   1.57   >93  83     66                                     2-methyl 2-propene 1-ol                                                                      1.47   1.54   >93  87     77                                     2-methyl 2-propene 1-ol                                                                      1.97   1.47   >93  82     67                                     2-methyl 2-propene 1-ol                                                                      2.48   1.47   >93  89     74                                     2-methyl 2-propene 1-ol                                                                      2.96   1.55   >93  76     64                                     2-methyl 2-propene 1-ol                                                                      3.9    1.75   >93  71     62                                     ______________________________________                                    

EXAMPLE 3

A polymerisable composition was used comprising 85 parts by weight of Diacryl D 121 and 15 parts by weight of 1,4-butanediol dimethacrylate which had been homogenised as described above. 0.5% by weight of cyclohexyl peroxydicarbonate was used as catalyst. The following results were obtained:

                  TABLE III                                                        ______________________________________                                         additive     %     Yi         p   E (150° C.)                           ______________________________________                                         allyl alcohol                                                                               0     2.54       86  106                                                       1     2.26       89  133                                                       1.5   2.2        89  115                                          ______________________________________                                    

EXAMPLE 4

A polymerisable composition was prepared using tetraethoxy bis-phenol A dimethacrylate sold by AKZO under the trade name Diacryl 121. This monomer was mixed with 0.5% by weight of cyclohexyl peroxidicarbonate. The compounds shown in Table IV were then introduced as additives to give the results indicated below.

                  TABLE IV                                                         ______________________________________                                                                         E      E                                       additive      %     Yi     p    (100° C.)                                                                      (150° C.)                        ______________________________________                                         2-methyl 2-propene 1-ol                                                                      10    1.73   >93                                                               8     2.06   >93  84.67  71.6                                                  5     2.13   >93  88.97  73.58                                   crotyl alcohol                                                                               5     2.36   >93  78.16  69.19                                   2-cyclohexene 1-ol                                                                           5     1.87   >93  49.34  53.42                                   ______________________________________                                    

EXAMPLE 5

Polymerisable compositions were prepared using the monomers shown in Table V.

                                      TABLE V                                      __________________________________________________________________________     Example                                                                              Monomer I                                                                            Comonomers II                                                                               Composition                                                                           Initiator                                      __________________________________________________________________________     5A    D121  isobornyl methacrylate                                                                      80/20  CHPC (0.5%)                                    5B    D121  benzyl methacrylate                                                                         80/20  CHPC (0.5%)                                    5C    D121  styrene      80/20  CHPC (0.5%)                                    5D    D121               100    CHPC (0.5%)                                    __________________________________________________________________________

The results obtained are shown in Table VI.

                  TABLE VI                                                         ______________________________________                                         Formulations  Yi after annealing                                                                          Yellow level                                        ______________________________________                                         A             2.32         4                                                   A + 2%        1.17         2                                                   methallyl alcohol                                                              B             2.3          4                                                   B + 2%        1.21         2                                                   methallyl alcohol                                                              C             1.75         3                                                   C + 2%        1.39         2                                                   methallyl alcohol                                                              D             4            4                                                   D + 2%        1.9          2                                                   methallyl alcohol                                                              ______________________________________                                    

Visual determination of the yellow level was carried out as follows:

level 0: corresponds to the colour of Orma without any addition of yellow dye (Orma is the trade name for a polymer material obtained from diethyleneglycol bis (allyl carbonate) manufactured by ESSILOR and used as a reference material:

level 1: Orma+0.0025% of yellow dye Neozapon 157;

level 2: Orma+0.01% of yellow dye Neozapon 157;

level 3: Orma+0.025% of yellow dye Neozapon 157;

The levels were determined in accordance with the following table. ##STR8##

EXAMPLE 6

A polymerisable composition was prepared using tetraethoxy bis-phenol A dimethacrylate sold by AKZO under the trade name Diacryl 121.

The compounds shown in Table VII were then introduced as additives in the proportions indicated. To this mixture, a photoinitiator was added in a proportion of about 0.1%.

The said photoinitiator is CGI 1700 or CIBA-GEIGY which is a mixture containing the following compounds: ##STR9## in a ratio B/A=75/25.

After casting in a mould, the mixture was irradiated by a mercury lamps during 5 minutes. An annealing was then carried out during one hour at 120° C. The final article has a thickness of 2 mm.

The additives shown in table VII are corresponding to the formula (IV) ##STR10##

                                      TABLE VII                                    __________________________________________________________________________     Additives R.sub.3                                                                            R.sub.4                                                                           R.sub.5                                                                            R.sub.6                                                                              R.sub.7                                                                            Yi % additive                                   __________________________________________________________________________     3-butene 2-ol                                                                            H   CH.sub.3                                                                          H   H     H   2.7                                                                               1.7                                          t,2-methyl 3-phenyl 2-propene 1-ol                                                       H   H  CH.sub.3                                                                                 H   1.8                                                                               3.8                                          carveol   Cycle                                                                              H  CH.sub.3                                                                           H     Cycle                                                                              1.2                                                                               3.7                                          myrtenol  H   H  Cycle                                                                              Cycle H   1.5                                                                               3.5                                          verbanol  Cycle                                                                              H  H   CH.sub.3                                                                             Cycle                                                                              2.3                                                                               3.5                                          t,cinammyl alcohol                                                                       H   H  H                                                                                   ##STR11##                                                                           H   1.65                                                                              3                                            3-methyl 2-butene              1.5                                                                               2                                            1-ol                                                                           Reference                      3.5                                                                               0                                            __________________________________________________________________________ 

We claim:
 1. A polymer composition obtained by polymerisation of a composition comprising:a composition A comprising: at least 50% by weight of a monomer or mixture of monomers having formula I: ##STR12## wherein R₁ and R₂, which may be identical or different, represent hydrogen or C₁ -C₆ alkyl, X represents: ##STR13## m and n are integers and m+n is between 0 and 10;0to 50% by weight or one or more mono- or poly-functional vinyl, acrylic or methacrylic comonomers (II); and a component B comprising:in a proportion of 0.5 to 15% by weight with respect to the weight of components (I) and (II), a monomer (III) comprising an ethylenic unsaturation which does not form part of an aromatic ring and containing, in position α of this unsaturation a carbon atom carrying a free hydroxy group.
 2. The polymer composition of claim 1, wherein the monomer (III) contains in position α of the unsaturation, a carbon atom carrying a free hydroxy group and being linked to at least one hydrogen atom.
 3. The polymer composition of claim 1, wherein the monomer (III) has formula (IV): ##STR14## wherein: R₃ and R₄ represent hydrogen or one of the groups R₃ and R₄ represent hydrogen while the other forms with group R₇ a C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups; or one of groups R₃ and R₄ may represent hydrogen while the other represents an aliphatic C₁ -C₆ alkyl group, a cyclic C₄ -C₁₆ hydrocarbon group or a C₆ -C₁₆ aromatic hydrocarbon group;R₅, R₆ and R₇, independently of each other, represent hydrogen or a C₁ -C₆ alkyl group which may be substituted by one or more OH groups, and wherein the chain may be interrupted by one or more ether, ester or ketone groups; an aromatic C₆ -C₁₆ hydrocarbon group or a cyclic C₄ -C₁₆ hydrocarbon group; R₇ may form with one of the groups R₃ or R₄ a C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups or one or more C₂ -C₄ alkylene groups; R₅ and R₆ may form a C₅ -C₁₀ ring which may be substituted by one or more C₁ -C₄ alkylene groups or C₂ -C₄ alkylene groups; two or more of the carbon atoms of the C₅ -C₁₀ ring formed with R₃ or R₄ and R₇ or with R₅ and R₆, may be bonded by a hydrocarbon bridge.
 4. The polymer composition of claim 3, wherein R₃ and R₄ represent hydrogen, R₅ represents methyl, R₆ represents hydrogen or methyl and R₇ represents hydrogen, methyl, ethyl or CH₂ OH.
 5. The polymer composition of claim 3, wherein the compound having formula (IV) is selected from the group consisting of allyl alcohol, methallyl alcohol, crotyl alcohol, 2-cyclohexene 1-ol, trans 2-hexene 1-ol, cis 2-butene 1,4-diol, and 3-methyl 2-butene 1-ol, trans 2-methyl 3-phenyl 2-propene 1-ol, 3-butene 2-ol, carveol, myrtenol, verbenol and trans- cinammyl alcohol.
 6. The polymer composition of claim 1, wherein the compound having formula I is used in proportions of between 70 and 100% by weight with respect to the weight of component A.
 7. The polymer composition of claim 1, wherein R₁ represents CH₃ and R₂ represents H and X represents ##STR15## m and n are integers and m+n is a whole number between 2 and 7, inclusive of 2 and
 7. 8. The polymer composition of claim 1, wherein the monomers having formula (II) are selected from the group consisting of phenyl(meth)acrylate, benzyl(meth)acrylate, phenoxyethyl(meth)acrylate and styrene or from the non-aromatic compounds which are selected from the group consisting of methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, isobutyl(meth)acrylate, butanedioldi(meth)acrylate and trimethylolpropane tri(meth)acrylate.
 9. The polymer composition of claim 1, wherein the compound having formula I is 2,2-bis (4-methacroyl oxdiethoxyphenyl)propane.
 10. The opthalmic lens made from a polymer composition according to claim
 1. 11. A lens assembly characterized in that it comprises at least one lens as defined in claim
 10. 12. A method of preparing a polymer composition as defined in claim 1 comprising:mixing one or more monomers having formula I and II and 0.5 to 15% by weight with respect to the weight of monomers having formula I and II of a monomer (III), and polymerizing the mixture.
 13. The method of claim 12, wherein the monomer (III)1 has formula (IV): ##STR16## wherein: R₃ and R₄ represent hydrogen or one of the groups R₃ and R₄ represent hydrogen while the other forms with group R₇ a C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups; or one of groups R₃ and R₄ may represent hydrogen while the other represents an aliphatic C₁ -C₆ alkyl group, a cyclic C₄ -C₁₆ hydrocarbon group or a C₆ -C₁₆ aromatic hydrocarbon group;R₅, R₆ and R₇, independently of each other, represent hydrogen or a C₁ -C₆ alkyl group which may be substituted by one or more OH groups, and wherein the chain may be interrupted by one or more ether, ester or ketone groups; an aromatic C₆ -C₁₆ hydrocarbon group or a cyclic C₄ -C₁₆ hydrocarbon group; R₇ may form with one of the groups R₃ or R₄ a C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups or one or more C₂ -C₄ alkylene groups; R₅ and R₆ may form a C₅ -C₁₀ ring which may be substituted by one or more C₁ -C₄ alkylene groups or C₂ -C₄ alkylene groups; two or more of the carbon atoms of the C₅ -C₁₀ ring formed with R₃ or R₄ and R₇ or with R₅ and R₆, may be bonded by a hydrocarbon bridge.
 14. A method of preparing a polymer composition of claim 1, wherein the polymerisation of the polymerisable composition in accordance with claim is carried out photochemically.
 15. A method of preparing a polymer composition of claim 1, wherein the polymerisation of the polymerisable composition is carried out by induction heating.
 16. An opthalmic lens made from a polymer resulting from a polymerisation of a polymer composition obtained by the method of claim
 12. 17. A polymerisable composition comprising at least 50% by weight of a monomer or mixture of monomers having formula I; ##STR17## wherein R₁ and R₂, which may be identical or different, represent hydrogen or C₁ -C₆ alkyl, X represents: ##STR18## m and n are integers and wherein m+n is between 0 and 10,0to 50% by weight of one or more mono- or poly-functional vinyl, acrylic or methacrylic comonomers (II); and a component B comprising:in a proportion of 0.5 to 15% by weight with respect to the weight of components (I) and (II) of a monomer (III) comprising an ethylenic unsaturation which does not contribute to an aromatic system and containing, in position α of this unsaturation, a carbon atom carrying a free hydroxy group.
 18. The polymerisable composition of claim 17, wherein the monomer (III) has formula (IV): ##STR19## wherein: R₃ and R₄ represent hydrogen or one of the groups R₃ and R₄ represent hydrogen while the other forms with group R₇ a C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups; or one of groups R₃ and R₄ may represent hydrogen while the other represents an aliphatic C₁ -C₆ alkyl group, a cyclic C₄ -C₁₆ hydrocarbon group or a C₆ -C₁₆ aromatic hydrocarbon group;R₅, R₆ and R₇, independently of each other, represent hydrogen or a C₁ -C₆ alkyl group which may be substituted by one or more OH groups, and wherein the chain may be interrupted by one or more ether, ester or ketone groups; an aromatic C₆ -C₁₆ hydrocarbon group or a cyclic C₄ -C₁₆ hydrocarbon group; R₇ may form with one of the groups R₃ or R₄ a C₅ -C₁₀ ring which may be substituted by one or more linear or branched C₁ -C₄ alkyl groups or one or more C₂ -C₄ alkylene groups; R₅ and R₆ may form a C₅ -C₁₀ ring which may be substituted by one or more C₁ -C₄ alkylene groups or C₂ -C₄ alkylene groups; two or more of the carbon atoms of the C₅ -C₁₀ ring formed with R₃ or R₄ and R₇ or with R₅ and R₆, may be bonded by a hydrocarbon bridge.
 19. A method of preparing a finished or semi-finished lens comprising casting a polymerisable composition according to claim 17 between two moulds having the required surface geometries and polymerising the composition.
 20. The polymerizable composition of claim 17, wherein the monomer (III) contains in position α of the unsaturation, a carbon atom carrying a free hydroxy group and linked to at least one hydrogen atom. 